FIELD OF THE INVENTION
The invention relates to a current sensor having a soft-magnetic magnet core on which, in addition to a primary winding in which a current to be measured flows, at least one secondary winding is wound into which an alternating current is fed that saturates the magnet core alternately in at least one direction, and an evaluation circuit which determines a flux produced in the magnet core by the primary winding.
German Published, Non-Prosecuted Patent Application DE 42 29 948 A1 describes a current sensor having a soft-magnetic magnet core with a primary winding and a secondary winding. An additional current source is connected in series with the secondary winding and sends a magnetization current through the secondary winding. The magnetization current alternately drives the soft-magnetic magnet core into positive and negative saturation. The soft-magnetic magnet core has an essentially square magnetization characteristic, so that a respectively constant current flows during a remagnetization between two saturation states, since an inductive impedance tends to infinity because of a virtually vertical shape of the magnetization characteristic. In the positive and negative half-cycles, that current in each case differs from a mean value by a value which is governed by the hysteresis of the magnetization characteristic. The influence of hysteresis in the magnetization loop can be compensated for by averaging the constant current flowing during the remagnetization during two successive half-cycles of different polarity, so that the measurement of the current flowing in the secondary winding during the time in which the magnet core is being remagnetized results in a current which is directly proportional to the current to be measured in the primary winding.